Hello, I am new to the forum. My rear diff is making noise and id like to repair it. Please see my photos. is this a 3.55 or 40.10. What does the 40.10 tag represent? do the 3.55 come with 4010 ring and pinion? i am new to this type of repair. any help would be much appreciated . Thanks

The tag you really need i sa little skinny on held on by two cover bolts. It will have numbers on it. There will be a tooth coung for the ring gear and pinion. Divide the smaller into the larger and that is the ratio, assuming no one has done any modifications

I have no idea what that little tag is for. 40.10 is not a gear ratio. The parts tag on the end of the axle is the right part number for your XJ. It says 3.55 and you have an open diif.

Hello, welcome!

The tag says the axle is the Chrysler 8.25 and your diff gearing is 3.55.

Regarding the noise, it could be anything. Popular culprit is pinion bearing though.

If changing gears, just make sure you know what you are getting yourself into. If you don't get it set up right, you'll know rather quickly. Pinion depth, pinion bearing preload, backlash, and carrier bearing preload. Either grenading the thing or a whine on decel for example.